Spectroscopic characteristics of Ti-indiffused sapphire

Interest in tunable solid state lasers has grown rapidly from the initial demonstration of sources based on vibronic transitions broadened by strong electron-phonon coupling, such as those found for many transition metal ions in crystalline hosts. The properties of transition metal ions in insulating matrices have received renewed interest since the first demonstration of the Ti:Al2O3 laser in 1982 [1]. This laser is based on electron transitions that can occur when a Ti3+ ion is introduced at an octahedral site, presenting well-understood spectroscopic characteristics when uniformly doped in a sapphire crystal during the growth process. The broad fluorescence band, high absorption cross section and short lifetime have been extensively studied. The progress made in the understanding of the basic optical spectroscopic properties of similar systems provide the basis for technological achievements in the laser field, with new materials covering the near infra-red region. In this paper, the spectroscopic properties of a sapphire crystal locally doped with Ti by thermal indiffusion in an inert atmosphere are presented. The fluorescence spectrum for a diffused sample is found to extend from a wavelength of approximately 600nm into the near infra-red, with a maximum at around 725nm, and exhibits significant polarisation dependence. The lifetime of the diffused Ti ions is measured to be 3.2 ±0.25 µs at room temperature. These results compare well with previously published data for bulk doped Ti:Al2O3 [2] Spatially resolving the fluorescence spectrum at a polished edge of the sample shows that the Ti ions are contained within 1 µm of the surface and these results will be discussed in the light of the Ti diffusion profile obtained by secondary ion mass spectrometry (SIMS). These results demonstrate that Ti ions may be introduced into sapphire by thermal indiffusion, and the fluorescence spectrum shows that a significant proportion of the Ti is incorporated in the trivalent state following the diffusion process. Local doping of Ti3+ by thermal diffusion in a sapphire host has enormous potential for the realisation of a broadly tunable active integrated optical source in a sapphire host